The mechanics of injury to the human knee is a complex process where external forces are transmitted to the lower extremity, the lower extremity responds causing displacements and rotations across the knee, stresses are induced in the soft tissues at and across the knee and, under some conditions, the tissues are disrupted. When the forces are not constant, prediction of the likelihood of injury and the severity of applied external forces is complex. The proposal presents a research program investigating to the knee that typically occur during snow skiing. Snow skiing is studied because the rate of injury to the knee is high, the forces transmitted to the foot by the ski can measured, and safety devices can reduce the high rate of injury. Specialized laboratory and field test apparatus has been, and is being, developed to measure and to analyze the forces and moments between the boot and the ski, the rotations and translations across the knee joint, and the EMG from muscle groups. The measurements are mad during laboratory and snow skiing experiments, and even during falling while skiing, when the likelihood of injury increases. The three translations and three rotations across the knee are recorded with a new instrument containing no linkage connections, thereby having no stick-slip and inertia problems typical of goniometers. The field measurements identify the injury environment and response of the knee during "typical" skiing. forces. The laboratory experiments clarify how the knee responds to dynamic The contributions of muscle contraction to models of knee translation and rotation and the likelihood of injury will be clarified. The concept of a bioadaptive safety device will be carried forward to the prototype stage. The "safety" function of this de vice will be controlled by the current contraction of the musculature. The common misconception that the forces of skiing are small compared to typical tibia fracture strength and knee alignment strength will be corrected. This erroneous concept is widespread, extending to standards organizations, the industry and the public alike. The conceptual error has a major impact on the design of safety devices, the evaluation and acceptance of safety devices, and the training and instruction given the public. Efforts are directed to the development of meaningful standards of safety at the national and international levels.